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Pioneer SX-636 issues

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danbiba

New Member
Hey guys, picked up a pioneer sx-636 and an SX-650 yesterday. Right off the bat on the 636 when it starts up it sounds great and then within a minute it starts to develop static on the right channel in every single mode(AM, FM, phono,aux). I'm thinking it's a cap that's causing the issue. I'm gonna dig into it more later today but wanted to know your thoughts in the meantime. Thanks
 
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danbiba said:
Hey guys, picked up a pioneer sx-636 and an SX-650 yesterday. Right off the bat on the 636 when it starts up it sounds great and then within a minute it starts to develop static on the right channel in every single mode(AM, FM, phono,aux). I'm thinking it's a cap that's causing the issue. I'm gonna dig into it more later today but wanted to know your thoughts in the meantime. Thanks
Click to expand...

Good Moring danbiba,

I would try cleaning the balance and all pots with Deox-IT 1st.

A bad cap could cause the static, but it only takes a few seconds for caps to be powered, and would most likely start when switched on. not sure if it would cause static after warming up, it would however effect the sound quality, allowing, or not allowing different freq to be pushed to the speakers.
If you are going to dig a little deeper into the amp, I would check all boards for swollen, or bad caps.

I'm no expert, but start with the easy, and work up to the more difficult issues if needed.

Nice score as well, the 650 is a great little guy, great sound quality for only 35w, and I really like the sleek look of the two indicator lamps on the dial board. Super clean receiver!

Good luck with the project! :thmbsp:
 
I doubt it is capacitor but maybe, those little sky blue caps are prone to failure.

The 636 has a bunch of notorious transistors that become leaky and become noisy. 2SA726 and 2SC1344 in the preamp can be replaced with KSA992 and KSC1845. 2SC1451 on the amps board need to go, replace with KSC3503. The differential pairs (two transistors at beginning of amp circuit with emitters tied together) should also be replaced with KSA992 preferably matched.

While your at it might as well give her a good recapping and enjoy it for another several decades. Is the noise volume dependent or is it loud regardless of volume?
 
Does it sound kind of "windy"? Like a microphone picking up wind noise? Had this happen with my 737 and thought the world was coming to an end. It was a bad transistor.

Ended up replacing everything with the help of this forum, the thing sounds amazing now.
 
I had cleaned out everything with deoxit last night, so I don't think it's the controls. And I realized today that after turning it on again it was there from the beginning,I guess I just didn't realize it at first yesterday. I was planning on recapping both of these units( the 650 has protection issues, but that's for another day) good to know about the transistors though I may have to check/change those also. Day had been crazy busy, but I did sneak a minute to open up the receiver and have a peek.... It seems like one of the main filter caps looks a tiny bit bloated,I may be seeing things but I'll check it. As far as the volume goes, the sound does get louder when you turn up the volume and disappears when the volume is all the way down. And I wouldn't say it's a "windy microphone" sound, more like a "consistently scratchy pot" sound.
 
danbiba said:
I had cleaned out everything with deoxit last night, so I don't think it's the controls. And I realized today that after turning it on again it was there from the beginning,I guess I just didn't realize it at first yesterday. I was planning on recapping both of these units( the 650 has protection issues, but that's for another day) good to know about the transistors though I may have to check/change those also. Day had been crazy busy, but I did sneak a minute to open up the receiver and have a peek.... It seems like one of the main filter caps looks a tiny bit bloated,I may be seeing things but I'll check it. As far as the volume goes, the sound does get louder when you turn up the volume and disappears when the volume is all the way down. And I wouldn't say it's a "windy microphone" sound, more like a "consistently scratchy pot" sound.
Click to expand...
If I were betting I'd say its the 2SA726 transistors on the preamp. Replace the caps and transistors on the preamp and the noise should go away.
 
The 1451's are more of a threat for absolute failure mode than the 726's, although both are. Both are a mandatory REPLACE without checking item. And the sooner the better. Start with the 1451's, test and then work back from the amp on the 726's and 725's(both 725 and 726 are replaced with the ksa992.)

Larry
 
Does anyone have a shopping list for all the transistors that normally need to be replaced along with with capacitors for a recap? I haven't had 2 minutes to sit down and figure out what I need, but I definitely want to order everything.
 
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Also just wondering, i can't seem to find a decent .33uf 25v Capacitor to replace the little blue caps on the amp board, any suggestions?
 
The KSA992FBU is fine. The suffix letters break down to hFe or GAIN (The F) and packaging (BU or Bulk).

As for the caps. Replace any that are less than 1uf with a stacked film cap. Try panasonic ECQ types. 50V cap won't hurt it.
 
Can i really replace a 25v Cap with a 50v? i was under the assumption that i could increase the Capacitance of a cap but not the Voltage.
 
voltage rating is for maximum the cap will work at .. capacitance is just that .its capacity or charge .
so voltage increase is fine up to a point ... keep capacitance the same .
 
So i purchased all my new caps and the replacement transistor. I was pretty sure i ordered all the right numbers for the transistors:


512-KSC3503DSTU
KSC3503DSTU
NPN Si Transistor x2

512-KSC1845FTA
KSC1845FTA
NPN Epitaxial Sil x4

512-KSA992FBU
KSA992FBU
PNP Epitaxial Sil x6

replacements for 2SC1451, 2SC1344 and 2SA726 respectively.

I started on the amp board and replaced the caps, which i've done a thousand times. Then i replaced the transistors on the board, which i've never done, but after many searches on google, mouser and taking tons of pictures i was cofident that i could install these the right way. Everything out and everything in, I fired up the unit to check my work. No explosions, thats good, but i selected my speaker output and turned up the volume a little and all i heard was a humming, and then a click and nothing. This happened on both channels and then there was nothing coming out of the speakers. i took out all the new transistors and replaced the old ones. still nothing, but if i turn the volume up i can hear music coming from the actual amp board.... this happened to me once before with my Onkyo TX-4500 and i was never able to figure it out. Guys, what have i done? haha
 
danbiba said:
So i purchased all my new caps and the replacement transistor. I was pretty sure i ordered all the right numbers for the transistors:


512-KSC3503DSTU
KSC3503DSTU
NPN Si Transistor x2

512-KSC1845FTA
KSC1845FTA
NPN Epitaxial Sil x4

512-KSA992FBU
KSA992FBU
PNP Epitaxial Sil x6

replacements for 2SC1451, 2SC1344 and 2SA726 respectively.

I started on the amp board and replaced the caps, which i've done a thousand times. Then i replaced the transistors on the board, which i've never done, but after many searches on google, mouser and taking tons of pictures i was cofident that i could install these the right way. Everything out and everything in, I fired up the unit to check my work. No explosions, thats good, but i selected my speaker output and turned up the volume a little and all i heard was a humming, and then a click and nothing. This happened on both channels and then there was nothing coming out of the speakers. i took out all the new transistors and replaced the old ones. still nothing, but if i turn the volume up i can hear music coming from the actual amp board.... this happened to me once before with my Onkyo TX-4500 and i was never able to figure it out. Guys, what have i done? haha
Click to expand...

I think you have installed transistors wrong, go back and check you work, all the transistors you replaced should be E-C-B from left to right looking at the front of the transistor. Mark has very detailed information on how to seat transistolrs properly, look for it. New transistors have different leg placements from 35year old components, check again. Attached link look at post # 67...

http://www.audiokarma.org/forums/showthread.php?t=159155&page=5
 
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So that being said have I done damage because I replaced the old transistors to where they were originally and it's still not working
 
could have burnt resistors or power supply is wrong . or you have caused a short .
then again if you have music inside the amp it may be that it cant get out because of the speaker fuses or switch is wrong position or speakers wired incorrectly . try in A speakers .
 
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